Thymoquinone
Also written 2-isopropyl-5-methyl-1,4-benzoquinone
Quick answer
The main constituent of the essential oil of nigella seed, falling as the seed is roasted and quickly destroyed by light; how much of nigella’s smell it accounts for has not been measured.
What it does
Thymoquinone makes up roughly a quarter to a half of the essential oil of nigella seed, with p-cymene and α-pinene the other main components. Abundance is not the same as odour impact, and the sources read do not establish what thymoquinone smells of in the seed: the handbook describes the crushed seed as reminiscent of lemon with a suggestion of carrot, and the distilled oil as unpleasant-smelling and tasting of juniper, without attributing either to a single compound.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- moderate
- Fat solubility
- high
- Water solubility
- moderate
- Heat stability
- low
Roasting nigella seed, conventionally or in a microwave, lowered its thymoquinone and p-cymene while pyrazines and furans rose, so toasted seed is chemically a different spice from raw. In laboratory solutions thymoquinone dissolved in water to about 0.55–0.67 mg per millilitre but degraded steadily there, fastest at alkaline pH, and light destroyed it in every solvent tested: less than a fifth remained after 24 hours of exposure, while samples kept dark held their concentration for 48 hours. Those were solutions of the pure compound; the study did not test seeds or seed oil.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- NigellaPrincipal component
The leading component of the seed’s essential oil, at roughly 25–50 per cent in the handbook’s account; the seed holds only about 0.5 per cent essential oil in all.
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Thymol
The names are close because the structures are related — thymoquinone carries the same methyl and isopropyl groups on a quinone ring that thymol carries on a phenol — but thymol is the phenol of thyme and ajwain, and thymoquinone the leading volatile of nigella.
Questions this page answers
- what is thymoquinone
- thymoquinone in nigella seed